I think the above posting possibly refers to the infamous Jubilee clip. It's a band of metal or plastic with a fluted surface. It is circular and has a key or screw attached which when turned, moves a gear along the fluted surface. This makes the band smaller or larger depending on which way you turn it.

Personally, I find a ridge of sticky tape easier and can add a decorative touch. I ripped cartiledges in my right wrist several years ago, losing all sensation in the ring and little fingers. I used the tape method to keep my fingers close to the bottom holes. With recorders (especially the plastic 'school' variety) it wasn't so bad, because they already have ridges moulded in. In the end I gave up the whistles and stuck to the recorder.

LTS